Reinhardt, Richard

‘Candidatus Phytoplasma cynodontis’ is widespread in bermudagrass and has only been found in monocotyledonous plants. Molecular studies carried out on strains collected in Italy, Serbia, and Albania enabled verification of molecular variability in the 16S ribosomal RNA (rRNA) gene. Based on restriction fragment length polymorphism and sequence analyses, the strains from Serbia were clearly differentiated from all others and assigned to a new ribosomal DNA (rDNA) subgroup designated as 16SrXIV-C. A system for amplification of fragments containing the ‘Ca. P. cynodontis’ groEL gene was developed to enable study of its variability in related strains belonging to different 16SrXIV subgroups. Despite the fact that the groEL gene exhibited a greater sequence variation than 16S rRNA, the phylogenetic tree based on groEL gene sequence analysis was highly congruent with the 16S rDNA-based tree. The groEL gene analyses supported differentiation of the Serbian strains and definition of the new subgroup 16SrXIV-C. Phylogenetic analyses of both genes confirmed distinct phylogenetic lineages for strains belonging to 16SrXIV subgroups. Furthermore, groEL is the only nonribosomal marker developed for characterization of ‘Ca. P. cynodontis’ thus far, and its application in molecular surveys should provide better insight into the relationships among these phytoplasmas and correlation between strain differentiation and their geographical distribution.

Analysis of the completely determined genomes of the plant-derived Acholeplasma brassicae strain O502 and A. palmae strain J233 revealed that the circular chromosomes are 1,877,792 and 1,554,229 bp in size, have a G + C content of 36 and 29%, and encode 1,690 and 1,439 proteins, respectively. Comparative analysis of these sequences and previously published genomes of A. laidlawii strain PG-8, ‘Candidatus Phytoplasma asteris' strains, ‘Ca. P. australiense' and ‘Ca. P. mali' show a limited shared basic genetic repertoire. The acholeplasma genomes are characterized by a low number of rearrangements, duplication and integration events. Exceptions are the unusual duplication of rRNA operons in A. brassicae and an independently introduced second gene for a single-stranded binding protein in both genera. In contrast to phytoplasmas, the acholeplasma genomes differ by encoding the cell division protein FtsZ, a wide variety of ABC transporters, the F₀F1 ATP synthase, the Rnf-complex, SecG of the Sec-dependent secretion system, a richly equipped repertoire for carbohydrate metabolism, fatty acid, isoprenoid and partial amino acid metabolism. Conserved metabolic proteins encoded in phytoplasma genomes such as the malate dehydrogenase SfcA, several transporters and proteins involved in host-interaction, and virulence-associated effectors were not predicted for the acholeplasmas.